Are stable nutrients at *proper levels* the key to growth and coloration? ?

[Oregon Grown Reef]

Proper levels being emphasized obviously. I haven't looked at any studies, but I'm curious to see what your opinions are on stable nutrients at proper levels being more important than we give them credit for. There have obviously been trends in the hobby that say we have too high or too low of a given nutrient, but the conflicting information overwhelms many and causes them to give less importance to stable nutrients at proper levels for their tanks. The longer I've had these same tanks running, the more I've been able to see how each change in levels of various kinds influences the corals overall health. I've had alk drift, albeit 0.4dkh over several months, and the corals don't respond negatively. However, I've seen corals not grow or lose color when nitrate is too high. When I say too high, that number may be different for each system, but each system has a number where it's too high. For me, when nitrate is over 10, I get browned out corals that grow slowly or not at all. After doing a large water change, in congruence with other nutrient reduction methods that have been in place for months, growth explodes and color returns. There are a few other changes I've made that I believe have contributed to the overall recent success, but each change has been for a specific problem. Color was addressed by doing a large water change and changing the lighting spectrum. I believe the wrong spectrum was mainly the reason for the corals not surviving long term, but nutrient levels to be the main contributing problem for color. Obviously lighting heavily impacts color, but I changed the lighting spectrum long before reducing nitrate from 12ppm to 8ppm and it wasn't until after the water change that the color started improving. As many are aware, phosphate isn't reduced very much via water changes. Phosphate hovers around 0.04-0.06ppm for me. For those wondering if it was possibly a contaminant or toxin, I run carbon 24/7 and do 2% auto water changes daily, so it's highly unlikely there's a contaminant. I've also had icp tests done that have shown nothing, but those are also limited in what they test for.

Interested in what your opinions are, but to me it also helps to know what kind of experience you have in the hobby. I've been keeping saltwater tanks for 6 years this December. I've been keeping coral since August 2018, so 4.5 years.

 

[jda]

What your corals are after is nitrogen and phosphorous, not nitrate and phosphate.

There is nearly no evidence that zoox can use nitrate and plenty that it does not, but some hosts can convert nitrate to a usable form or nitrogen at a LARGE cost of 30-70% more energy. Most coral get their nitrogen from ammonia. So, having nitrate just means that the ammonia that the coral grabbed as the nitrate rose did the heavy work. If you keep the ammonia the same, then nitrate can be lower - my sand bed turns no3 into nitrogen gas like it's it's job.

I have been reading a lot lately about phosphorous and dinos/zoox. I have more to read, but so far it seems that we don't really have any idea what is going on except that there are multiple sources. Our test kits test for orthophosphate only. Zoox can use some of this, but not nearly as much as metaphosphate and organically bound phosphorous. What you test and what is available for your corals is not the same thing. It appears that most corals in mature tanks get lots of their phosphorous through absorbing bacteria and other waterborne micro things through their slime coats and not with orthophosphate - the corals do this very efficiently and keep a lot of the energy and building blocks. Zoox do gather metaphosphate and use it for phosphorous and also to remove contaminants with the other compounds that are attached. Some coral can catch and digest actual food with the mouths, but this appears inefficient in our tanks since we don't have the right food to feed them - live zooplankton - but they also use energy to digest and sometimes spend more than they earn.

Hosts can recycle building blocks for their symbionts.

In the end, heavy input and heavy export has always worked and still does. I know that testing for no3 and po4 is easy, but it appears to be fools gold. Feed your fish a lot and skim heavy, have a fuge and keep your water changed to encourage micro fauna to grow with the traces. Water changes to lower po4 and no3 seem like a drop in the bucket, but they have other uses that are very important, IME. My tank has about .1 no3 and 1-3 ppb on po4, but I assure you that there is a massive amount of nh4 and non-testable sources of phosphorus in my tank. Corals grow like crazy. Ocean does it this same way, it seems.

Stability? I don't know. Probably. The thing is that we cannot test for what you want to keep stable. Stability isn't always necessary, but it also means that you don't drop or spike, so if you are stable, then you don't crash. My guess is that most true coral can have periods of growth when they can gather excess building blocks and energy and just maintain when they cannot by recycling.

 

[martyumengan]

This is a good read regarding the loss of color of some corals when exposed to elevated nitrate levels, while starving on P:

Unravelling the different causes of nitrate and ammonium effects on coral bleaching

The paper also supports jda's reply:

Nitrate enrichment has been shown to increase or prolong coral bleaching under thermal stress, especially with limited phosphorus availability14,15,17. More specifically, nitrate enrichment coupled with phosphorus starvation can result in changes in the algal lipid composition and destabilization of thylakoid membranes under increased light and temperature conditions14. On the other hand, moderate ammonium enrichment can be an important DIN source for maintaining photosynthesis and photosynthate translocation or calcification and delaying bleaching during thermal stress.

 

[Subsea]

In my experiences of 51 years of reefkeeping, photosynthesis is not controlled by the most abundant nutrient, but it is limited by the least abundant trace mineral (nutrient).